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Sunscreen Safety Debates Continue. Next Talking Point: BOS

Published April 25, 2024
Published April 25, 2024
Allison Saeng via Unsplash

Mineral sunscreens have come a long way from being chalky, thick, gloopy creams with more flashback than a studio camera setup. With increasing concern about certain chemical filters, whether around the potential health risks due to absorption or reef damage, mineral formulations swooped in as the safer alternative, especially for those with sensitive skin.

Butyloctyl salicylate (BOS) is a booster partially responsible for the more cosmetically elegant mineral formulas, while also upping a sunscreen’s protection level against ultraviolet rays. A recent Bloomberg article has called into question the safety of this booster.

The chemical family of salicylates has been the source of some controversy: in 2018, salicylic acid (the ingredient BOS is derived from) was classified as a Category 2 reproductive toxicant, but topical treatments containing 2% or less salicylic acid were deemed safe. But especially for those who are pregnant, the ingredient needs to be approached with caution to prevent potential fetal damage.

BOS has a similar chemical structure as octisalate (one of the chemical filters that was absorbed at a higher rate than previously assumed). On first glance, consumers using a mineral sunscreen to avoid chemical filters, only to end up with a product that has molecules with an octisalate-adjacent profile, may feel worried. However, BOS is prevalent across both mineral and chemical formulas. “We should remember that BOS has been used for a long time in chemical sunscreens to begin with, in part because it helped to mitigate some of the degradation that was associated with the way that avobenzone can be used in formula,” Kevin Cureton, COO of Solésence, tells BeautyMatter.

Unpacking the Chemistry of Filters and Boosters

Product developer and CEO of Grace Kingdom Beauty Ginger King tells BeautyMatter: “Both [butyloctyl salicylate and octisalate] are in their ester form, ending in ate, which means they can be converted to salicylic acid, which can have penetration issues. However, BOS is usually used as a carrier solvent/booster, so the amount is limited to 5%. If this becomes an approved drug active, the usage will be higher and then the safety profile will need to be reviewed. To me, the risk is percentage-dependent and also depends on the formulation to see if there are chances to convert from the ester to acid form.”

However, BOS’s larger molecular size makes a case for its consumer safety. “Weight matters when you think about these materials. The structure of BOS and the ability for it to be absorbed through the skin is different. While they are in the same [chemical] family, as you go up in molecular weight it will change the properties and performance,” Cureton comments.

“Any material like zinc, in your diet or an aquatic environment, at extraordinary levels, they could function as if it were a poison,” Cureton adds. Titanium dioxide has raised concern around respiratory elements, mainly its nanoparticles being possibly carcinogenic and mutagenic, although there is still ongoing research needing to be done. “That story is still being figured out. People are being pretty safe in terms of mitigating it as a respirable form. All the work that we've done in any of the formulas that we supply that contain titania are in a non-respirable form. We've tried to be pretty safe from that standpoint, in terms of making sure that we mitigate risks,” he adds. King points out that the bigger safety issue is for people handling the raw materials for zinc oxide and titanium oxide products when it comes to nano-sized variations, which speaks for non-nano options. 

As an expert in the sunscreen industry, the COO has seen numerous conversations come and go around safety, including non-nano versus nano zinc. Here too, consumer conversations influenced the course of the market. “We don't believe that nano is bad, but if consumers are going to not buy something because they have a perception that it's bad, then maybe the market should just go ahead and not use it,” he proclaims.

“Ultimately, finding the perfect sunscreen formula is a congruence of performance, safety, environmental impact, and aesthetics.”
By Kevin Cureton, COO, Solésence

To Boost or Not To Boost, That Is the Question

While BOS improves the SPF protection level, it is a small boost. Due to the efficacy of their zinc oxide, Solésence’s formulas don’t require a high level of boosters. Some formulas don’t contain any BOS whatsoever. “We increasingly have clients who ask for a second option of high SPF without BOS in the formulation. When you look at the in vitro analysis of our formula and the level of contribution to SPF performance only through boosting, BOS is not an effective sunscreen active by itself. The thing that we always have to remember when we look at SPF measurement in particular is that it's a log system. Going from an SPF 30 to an SPF 50 is only a percent or two more in UV protection. So the type of contribution that you're seeing from both sides is modest at best,” Cureton states.

To reach an SPF of 30 as a mineral formula often requires 15-16% zinc and titanium dioxide with an average of 5% BOS. Anything above 5% would make an active ingredient and therefore be subject to different regulations. Cureton is seeing a slight uptick in requests for BOS-free formulas, but also emphasizes this is partially due to the forward-thinking customer Solésence serves, who is more deeply invested in ingredient awareness. For those seeking formulas without the booster, there are alternatives to make sure shoppers don’t have to sacrifice on product skinfeel.  Alternatives include using a higher percentage of zinc to reach a level of SPF with no booster necessary.

99% of Solésence's formulation work is with zinc oxide. “Zinc oxide has a great safety profile. Where people have raised concerns typically would be with zinc oxide used in an uncoated form, and it could be contributing to free radicals that could be damaging to formulas or skin and then certainly could be damaging to coral reef. What we've done and that's really at the heart of our technology, is created a form of zinc oxide, that is essentially a radical puncher. It doesn't contribute in the same way to the concerns that people would have around free-radical damage that can occur,” Cureton explains.

Neither Cureton nor King have seen data on the coral reef impact of the material. Due to BOS not being a sunscreen active, there probably hasn’t been much imperative to research it this extensively. The dose makes the poison, which is why any studies need to be explored beyond surface (or shock) value. “It should have been assessed prior to approving it,” says King. 

In the future, further investment and research into these ingredients and their safety will be paramount, aided by the increase in consumers purchasing and using these products on a daily basis. “SPF is still a niche business generally in comparison to the rest of the beauty industry. It's growing rapidly, obviously, but at the end of the day, because it's not there yet, people don't invest in them in the same way they might invest in other spaces. That is one of the reasons why we invest north of 6% of our revenue on R&D,” he says. While UV protection is non-negotiable, it is now additional factors like free radicals (“one of the fundamental ways that skin and particularly structural elements of skin gets damaged or mutations like cancerous lesions can be generated”) and environmental impact of certain ingredients that Solésence is looking at. The company’s latest research includes plant-based sunscreen active chemistry. At Biofabricate, other innovators were showing melanin-based UV filters are other future potential options.

Perhaps an even bigger point of discussion should be reapplication. Most sunscreen labels mention reapplying every two hours, but how can consumers do this without disrupting their makeup or their skin becoming too heavily saturated with products? Touch-up tools like SPF-containing powder or sprays are available, but trials have shown that the level needed for adequate SPF coverage could result in powdery or greasy skin—most consumers aren’t applying enough product for advertised levels of protection.

“We have increasingly started to talk to our brand partners about if you're building this beautiful skincare or complexion product, what's your plan for re-application? We think that it's increasingly something that the industry is going to lean into,” Cureton says. “Ultimately, finding the perfect sunscreen formula is a congruence of performance, safety, environmental impact, and aesthetics.”

Better Formulas, Better Safety

While there is more research that needs to be done into filters and boosters of many varieties, the cosmetic elegance that BOS provides for formulas has one undoubtable benefit: customers are more likely to use the product.

“At the end of the day, people absolutely want the products to be effective, but they want them to feel good and feel great,” Cureton says. “If you look at the growth of the use of SPF-containing [mineral] formulas, it's because people are now seeing that as a significantly better option than some of the chemical filters that are available. But the best SPF is the one that people are going to use every day. If that means that some people are using a chemical-based sunscreen, then that's way better than not using anything.”

“Better spreadability helps with sensory appeal—if the consumer does not like how the formula spreads on them, they will not use the products. A continuous film on the skin also can help with SPF protection,” adds King. Furthermore, due to BOS helping mineral filters go the extra mile, it can also help with reducing flashback issues as formulators don’t have to push mineral filter levels as high.

The different levels of legislation worldwide are also proving a challenge to finding a universal safety standard in sunscreen. In the US, Canada, and Australia, sunscreens are classified as a drug, whereas elsewhere they are considered cosmetics. 

“One of the things that you hear a lot about in the US related to sunscreens is look at how many more sunscreens are available in Europe and Asia. Then on the other side, they'll say, look at how many ingredients are not banned in the US, that's a very short list. Let's make sure we understand what that conversation is suggesting, because it shouldn't suggest that a long or a short list is the right list. You need to make sure that things are safe and effective, period. You’ve got to make sure that you're doing the right thing and following the right guidance relative to keeping people healthy and helping them feel as wonderful and as beautiful as they would like to,” Cureton adds.

The conversation around BOS is an important reminder that our industry needs to head towards a fact-based, safety-informed conclusion to create clarity for the industry and consumers alike. “We should really make sure that the science is not biased. You want to have independent, verifiable data behind what you do and what you say. That's an important part of making sure people are really trusting what we do as an industry. You never want to lose that credibility,” Cureton emphasizes.

King concludes, “At the end of the day, consumers buy to solve a problem. People buy sunscreen to prevent sun damage, but if they do not like how it wears, they will not use the product. As far as clients are concerned, yes, safety is a top priority, but until you can prove BOS is bad, consumer benefits rule every time.This is a bit like how petrolatum is not regarded highly in the clean beauty space, but there are still award-winning products with petrolatum. It's consumer preference!”


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